1. Field of the Invention
The present invention relates to a packaging structure for plural bare light-emitting chips and, more particularly, to a packaging structure that achieves high illuminous efficiency as well as low manufacture cost.
2. Description of the Related Art
Referring to FIG. 1, a cross-sectional view of a conventional LED packaging structure is shown. The LED packaging structure has a substrate 91, a plurality of bare LED chips 92, and a light guide 93. The substrate 91 supports the bare LED chips 92 and light guide 93, and may have circuits connecting with and for operating the bare LED chips 92. Each bare LED chip 92 may receive electrical power and then emit light, which has a light-emitting face 921 facing away from the substrate 91 and able to emit the light. The light guide 93 is made of transparent material, covers and seals up the bare LED chips 92, and connects with the substrate 91. Particularly, a side of the light guide 93 facing away from the substrate 91 forms a semi-spherical surface 931 to gather the light emitted by the light-emitting faces 921 of the bare LED chips 92 to enhance the illuminous efficiency in a predetermined direction.
However, the above conventional LED packaging structure has the following drawbacks. First, when the bare LED chips 92 are operated, a thickness of the light guide 93 between the semi-spherical surface 931 and the light-emitting faces 921 results in low dissipation efficiency of heat generated by the operated bare LED chips 92. Accumulation of heat will seriously affect the efficiency of light emission of the bare LED chips 92 after a continuous operation of the bare LED chips 92, which can even damage the bare LED chips 92. Second, the light guide 93 has to be made by transparent material not easy to deteriorate by heat, which is expensive, so as to suffer the heat of the operated bare LED chips 92 without deterioration, and thus reducing the volume of the light guide 93 is an efficient way to lower the cost of manufacture. However, in order to maintain a sufficient illuminous efficiency, the thickness of the light guide 93 between the semi-spherical surface 931 and the light-emitting faces 921 should be held and thus limits the reduced cost of manufacture. Besides, as the amount of the bare LED chips 92 increases, the diameter of the semi-spherical surface 931 and the volume of the light guide 93 must largely increase to completely cover all the bare LED chips 92 since the total area of the light-emitting faces 921 increases. Therefore, the above said two drawbacks go worse as the amount of the bare LED chips 92 increases.
In light of this, it is desired to improve the conventional LED packaging structure to maintain a preferable illuminous efficiency as well as enhance the heat-dissipating efficiency and lower the manufacture cost.